Transition-metal-based molecular complexes are a class of catalyst materials for electrochemical CO2 reduction to CO that can be rationally designed to deliver high catalytic performance. One common ...mechanistic feature of these electrocatalysts developed thus far is an electrogenerated reduced metal center associated with catalytic CO2 reduction. Here we report a heterogenized zinc–porphyrin complex (zinc(II) 5,10,15,20-tetramesitylporphyrin) as an electrocatalyst that delivers a turnover frequency as high as 14.4 site–1 s–1 and a Faradaic efficiency as high as 95% for CO2 electroreduction to CO at −1.7 V vs the standard hydrogen electrode in an organic/water mixed electrolyte. While the Zn center is critical to the observed catalysis, in situ and operando X-ray absorption spectroscopic studies reveal that it is redox-innocent throughout the potential range. Cyclic voltammetry indicates that the porphyrin ligand may act as a redox mediator. Chemical reduction of the zinc–porphyrin complex further confirms that the reduction is ligand-based and the reduced species can react with CO2. This represents the first example of a transition-metal complex for CO2 electroreduction catalysis with its metal center being redox-innocent under working conditions.
Abstract
Broken symmetries play a fundamental role in superconductivity and influence many of its properties in a profound way. Understanding these symmetry breaking states is essential to elucidate ...the various exotic quantum behaviors in non-trivial superconductors. Here, we report an experimental observation of spontaneous rotational symmetry breaking of superconductivity at the heterointerface of amorphous (a)-YAlO
3
/KTaO
3
(111) with a superconducting transition temperature of 1.86 K. Both the magnetoresistance and superconducting critical field in an in-plane field manifest striking twofold symmetric oscillations deep inside the superconducting state, whereas the anisotropy vanishes in the normal state, demonstrating that it is an intrinsic property of the superconducting phase. We attribute this behavior to the mixed-parity superconducting state, which is an admixture of
s
-wave and
p
-wave pairing components induced by strong spin-orbit coupling inherent to inversion symmetry breaking at the heterointerface of a-YAlO
3
/KTaO
3
. Our work suggests an unconventional nature of the underlying pairing interaction in the KTaO
3
heterointerface superconductors, and brings a new broad of perspective on understanding non-trivial superconducting properties at the artificial heterointerfaces.
Understanding how remarkable properties of materials emerge from complex interactions of their constituents and designing advanced material structures to render desired properties are grand ...challenges. Metal–oxide interactions are frequently utilized to improve catalytic properties but are often limited to situations where only one component is facilitated by the other. In this work, we demonstrate highly cooperative win-win metal–oxide interactions that enable unprecedented catalytic functionalities for electrochemical CO2 reduction reactions. In a single SnO x /Ag catalyst, the oxide promotes the metal in the CO production mode, and meanwhile the metal promotes the oxide in the HCOOH production mode, achieving potential-dependent bifunctional CO2 conversion to fuels and chemicals with H2 evolution suppressed in the entire potential window. Spectroscopic studies and computational simulations reveal that electron transfer from Ag to SnO x and dual-site cooperative binding for reaction intermediates at the SnO x /Ag interface are responsible for stabilizing the key intermediate in the CO pathway, changing the potential-limiting step in the HCOOH pathway, and increasing the kinetic barrier in the H2 evolution pathway, together leading to highly synergistic CO2 electroreduction.
Psoriasis and parapsoriasis en plaques are chronic inflammatory skin diseases, both representing therapeutic challenge in daily practice and adversely affecting the quality of life. Reactive oxygen ...species (ROS) has been evidenced to be involved in the pathogenesis of the chronic inflammatory diseases. We now report that hydrogen water, an effective ROS scavenger, has significant and rapid improvement in disease severity and quality of life for patients with psoriasis and parapsoriasis en plaques. At week 8, our parallel-controlled trial revealed 24.4% of patients (10/41) receiving hydrogen-water bathing achieved at least 75% improvement in Psoriasis Area Severity Index (PASI) score compared with 2.9% of patients (1/34) of the control group (Pc = 0.022, OR = 0.094, 95%CI = 0.011, 0.777). Of patients, 56.1% (23/41) who received bathing achieved at least 50% improvement in PASI score compared with only 17.7%(6/34) of the control group (P = 0.001, OR = 0.168, 95%CI = 0.057, 0.492). The significant improvement of pruritus was also observed (P = 3.94 × 10
). Besides, complete response was observed in 33.3% of patients (2/6) of parapsoriasis en plaques and partial response in 66.7% (4/6) at week 8. Our findings suggested that hydrogen-water bathing therapy could fulfill the unmet need for these chronic inflammatory skin diseases.
Conspectus Molecular catalysts, often deployed in homogeneous conditions, are favorable systems for structure–reactivity correlation studies of electrochemical reactions because of their well-defined ...active site structures and ease of mechanistic investigation. In pursuit of selective and active electrocatalysts for the CO2 reduction reactions which are promising for converting carbon emissions to useful fuels and chemical products, it is desirable to support molecular catalysts on substrates because heterogeneous catalysts can afford the high current density and operational convenience that practical electrolyzers require. Herein, we share our understanding in the development of heterogenized metal phthalocyanine catalysts for the electrochemical reduction of CO2. From the optimization of preparation methods and material structures for the electrocatalytic activity toward CO2 reduction to CO, we find that molecular-level dispersion of the active material and high electrical conductivity of the support are among the most important factors controlling the activity. The molecular nature of the active site enables mechanism-based optimization. We demonstrate how electron-withdrawing and -donating ligand substituents can be utilized to modify the redox property of the molecule and improve its catalytic activity and stability. Adjusting these factors further allows us to achieve electrochemical reduction of CO2 to methanol with appreciable activity, which has not been attainable by conventional molecular catalysts. The six-electron reduction process goes through CO as the key intermediate. Rapid and continuous electron delivery to the active site favors further reduction of CO to methanol. We also point out that, in homogeneous electrocatalysis where the catalyst molecules are dissolved in the electrolyte solution, even if the molecular structure remains intact, the actual catalysis may be dominated by molecules permanently adsorbed on the electrode surface and is thus heterogeneous in nature. This account uses our research on CO2 electroreduction reactions catalyzed by metal phthalocyanine molecules to illustrate our understanding about heterogeneous molecular electrocatalysis, which is also applicable to other electrochemical systems.
Single crystals of 2H-NbS2 are prepared by chemical vapor transport method under varying conditions. The residual resistivity ratio (RRR) of the as-grown single crystals is observed to change from 10 ...to 60, while the superconducting transition temperatures (Tc) remain around 6.2 K. Changes in stoichiometry were obtained by annealing in different conditions, resulting in sulfur deficient 2H-NbS2−y single crystals. Both Tc and RRR of the annealed samples are found to drop drastically when y increases from 0.05 to 0.10, which is argued to be the effect of enhanced electron scattering caused by the decreased interlayer coupling evidenced by the increase of the c-axis lattice constant after annealing, possibly due to Nb intercalation between layers.
Electrocatalysts that start a reaction as molecules do not always end the reaction as molecules, and even when they do, they might not be molecules during catalysis. In this Perspective, we discuss ...knowledge learned from the study of Cu‐based molecularly structured electrocatalysts––including metal coordination complexes, metal‐organic frameworks, single‐atom catalysts, and polymeric materials––that restructure under electrochemical CO2 reduction reactions. Recent reports are summarized with an emphasis on the nature and significance of post‐mortem and in situ characterization for the proper identification of active sites. We demonstrate that molecular and material structures determine whether electrocatalysts restructure and how they restructure, that understanding of restructuring processes can help us identify active sites for catalysis, and that this knowledge can be leveraged to design precatalysts that generate highly active catalysts under reaction conditions. In addition, we provide recommended practices for studying the integrity of heterogeneous molecular catalysts during and after CO2 reduction reactions.
Key Points
Heterogeneous molecular Cu catalysts have been observed to restructure to metallic Cu clusters under reaction conditions.
Dynamic or reversible restructuring confounds identification of real active sites.
Both ex situ and in situ techniques are recommended for robust catalyst characterization.
Observed restructuring of heterogeneous molecular electrocatalysts necessitates careful post‐mortem and in situ characterization to identify real active sites.
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